flattenObjectArray

flattenObjectArray.js

const data = [

    { "itemSelected": "item1", "data": "2017-09-12", "descricaoPrestacao": "desc1 item1", "valor": 1 },

    { "descricaoPrestacao": "desc2 item2", "valor": 2, "itemSelected": "item2", "data": "2017-09-12" },

    { "descricaoPrestacao": "desc3 item3", "valor": 3, "itemSelected": "itemMIL", "data": "2017-09-12" },

    { "descricaoPrestacao": "desc2 item1", "valor": 1, "itemSelected": "item1", "data": "2017-09-12" },

    { "descricaoPrestacao": "desc2 item2", "valor": 2, "itemSelected": "item2", "data": "2017-09-12" }

]

const flatten = (obj) => {
    return obj.reduce((acc, el) => {
        acc[el.itemSelected]
            ? acc[el.itemSelected] += el.valor
            : acc[el.itemSelected] = el.valor
        return acc
    }, {})
}

const makeArray = (obj) => {
    return Object.keys(obj)
        .reduce((acc, el) =>
            acc.concat({
                [el]: obj[el]
            }), [])
}

console.log(makeArray(flatten(data))) // [ { item1: 2 }, { item2: 4 }, { itemMIL: 3 } ]